Nickel plated honeycomb panel



June 14, 1960 T. A. HERBERT, JR 2,940,557

I NICKEL PLATED HONEYCOMB PANEL Filed Sept. 20, 1955 3 Sheets-Sheet 1 INVENTOR. T.A.HER.BRTJ.

ATTORNEY June 14, 19 0 T. A. HERBERT, JR 2,940,557

NICKEL PLATED HONEYCOMB PANEL Filed Sept. 20, 1955 3 Sheets-Sheet 2 ATTORNEY 3 Sheets-Sheet 3 ATTOJPNE 1" June 14, 1960 T. A. HERBERT, JR

NICKEL PLATED HONEYCOMB PANEL Filed Sept. 20, 1955 a, 1 R M m T fi i m m .w V B 6 5 A 0 I J W w a 9 3 w W H a ON 1 4 5 a 4 3 fi NICKEL PLATED HONEYCOMB PANEL Thomas A. Herbert, in, Chula Vista, Califi, assignorto Rohr Aircraft Corporation, Chula Vista, Calif., a corporation of California Filed Sept. 20, 1955, Ser. No. 535,343

1 Claim. Cl. 189-34) This invention is an improvement on that shown in my pending app1ication. Serial No. 501,820, filed April 18, 1955. The aforesaid application discloses a method for brazing a central honeycomb core to two metal skins .or plates to make a sandwich panel by inserting a thin foil of brazing metal between the core and each skin andheating the assembled sandwich to the fusion temperature of the foil. It has been found that the brazing metal attaches itself more easily to the core and skins and makes a stronger bond between the component parts if the skins and core have previously been coated with a thin plating of suitable metal of high melting point. I

it is accordingly a purpose of my invention to .provide such a coating by electrically plating a thin layer of substantially pure nickel on both the core and skins prior to assembly of the sandwich.

In cases where a doubler member is used around the edge of the panel to project beyond the core and provide a means for connecting the panel to anotherstructure in an assembly, it isa further object of the invention toprovide an electrically plated coating on the doubler.

Also in cases where the edge of the honeycomb core is to be surrounded and enclosed by a metal closure member, a further object is to plate such closure member with a thin plating of metal whichbecomes securely bonded to the closure member and core and assists in securing a strong brazed joint between the members.

Other objects will become apparent as the description of the novel method of making a honeycomb panel proceeds. For a better understanding of the invention, reference is made to the accompanying drawings, in which: Figs. .1 and 2 areschematicdrawings of apparatns used for el pl fi mp n parts of a hqn v bmb Panel;

e 3 is a fragmentary e p v View P r n se tion of a portion or" a sandwich panel;

Fig. 4 is an enlarged view taken on line of Fig} sh w a portion o the ,Pamlan with h icknes the nickel plating exaggerated for clarity; i

' Fig. 5 is a perspective view ,of asupporting fintureon wh a sa dw panel h ing u d urfaces $12 po ted w se io o both .pa n --fi f @1 1 why to show detailsof their construction; il 4 Fig. 6 is a cross sectional yiewof Fig. 5 takenon line -s;

fig. 7 is a schematic drawing of the apparatus used o in t pa 0. a h eyco P n t her; and

Fig. 8 isan enlarged fragmentary sectional view of the sandwich panel taken through a eomrnon side wall of adjoining cells. i V

After cleaning in any known manner, .two sheets of sta inless steel 26, 27 and a cellular honeycomb core 25 also made of stainless steel, are immersed in a plating bath 59 containedina tank 601(Fig. 1- The sheetsand core are preferably maderof 17,-7.1?Hstainlees steel hay ing approximately the composition 1 nited States Patent f) 1 if 2 A nickel anode 61 in the bath is connected to the positive terminal of a direct current'geuerator 62 and the sheets and .core'to the negative generator terminal. Bath 59 preferably has the composition Y Ounces per gallon Nickel chloride, N iCl -6I-I;,O.. 32 Boric acid, H BO 7 q 7 5 Hydrochloric acid, HCl 4 Water. 7 i balance although other known nickel salt solutions capable of forming a thin strike plating .on the parts may be used instead. With bath 59 at a temperature of about 70 F. and using a current density of between 20 to 40 amperes per square foot, in from 60 to seconds core 25 and plates 26, 27 .are completely covered with a thin strike plating of nickel which adheres strongly to the'surfaces of the parts.

The'plated parts are taken out of bath 59 and immediately placed in a nickel plating bath 63 contained in a tank 64. A nickel anode .65 in bath 63 isconnected to the positive terminal of a direct current .generator 66 and the plated core 25 and sheets 26, 27 to its negative terminal. Bath 63 is preferably kept at a temperature between and F. by heat supplied to tank 64 by any suitable heater, such as a gas burner 67.

Plating .solution 63 preferably has the composition:

Ounces per gallon panel 10 having a compound curved surface is shown supported on'a fixture l1 preparatory to the brazing op eration. Fixture 11 comprises a rigid metal lattice 12 composed of fiatmeta-l bars 13 intersecting each other at substantially right angles to form a series of cells 14. The walls of cells 14 are provided withopenings 15 therethrough which permit ,air to circulate freely throughout lattice 12. The upper Surface 16 of the lattice is machinedto thecontour of the panel to be supported thereon, and is covered by a steelsheet 17 which is formed to the contour of surface 16 to provide a smooth continuous surface for supporting panel It}. A rigid frame 1-8 completely surrounds lattice 12 and isrigidly connected theretoby a set of connecting ribs 19. A metal molding 20 having a smooth rounded face 21 blending with sheet 17 and extending out beyond frame 18 surrounds lattice 12 and is supportedby frame 18. Lattice 12 issupported on I beams 22 the upper faces 23 of which are provided with openings 24(Fig. 6) communicating with cells 14.

Panel 10 comprises the nickel plated cellular core 25 positioned between the nickel plated upper skinor sheet 26 and the nickel plated lower sheet 27 with the walls of the honeycomb cells disposed transversely to the surfaces of skins26, 27. The upper face of the panel is undercut as indicated at 69 (Fig. 4) all around itsedge to receivea rickel plated metal sheet or doubler 68, -,a thin strip 70 of brazing alloy being interposed between the undercut edge 69 of core 25 and the upper horizontal extension 71 of closure member30 which entirely surrounds core 25. Abutting strips 29 (Figs! 3 and 4) of brazing alloy cover the remainder of the top of core 25 and a st rip or strips 29 of brazing alloy are interposed between the bottom of core 25 and lower plated skin 27.

, A continuous strip 72 of brazing alloy is interposed 'between the edge of core 25 and the vertical limb 73 of member 30. It has been found that by making the strips 70,29, 29'a and.72 aboutQfiOZ inch thick from an'alloy consisting of 85 percent silverand'lj percent manganese,

the assembled parts of the panelbecome strongly secured 7 together when heated to a temperature of about 1800 F.

If the'parts of'the' panel are made of material other than stainless steel; "a brazingalloy .is used which will fuse and adhere to the nickel plating" at a temperature considerably'below the melting point of the metal'composing core 25 and skins 26 -27." Member 30 may be one of various shapes in cross section such as a U shape or Z shape, as shown, and is for the purpose of providing a a a 4 r of known type operated by compressed air supplied by a source (not shown) through an air line'50, for thepurpose of withdrawing air from within sealed envelope 34. In-

let tube 38 is connected to a source 51 of dry hydrogen or other inert gas and is provided with a regulator 52to control the amount of gasEentering envelope 3 4 therethrough.--'-A-section of tube 38'withinthe furnace 46 is formedjin aspiral'coil53and a' section outside of the furnace is'formed 'in a spiral coil 54 to provide means for heating the hydrogen gas as it passes through 'coil'54: Coil 54 is heatedbyqits resistance to anelectrical current passing therethrough between connections 55 attached to tube 38 at each end 'of coil'54 and which are connected with. the secondary windingtof an electrical transformer closure .around the 'edge of the core and also a projection I shown) which comect the panel to another structure. If desired, a strip of brazing 'alloy (not shown) may be inserted betweenthe lower face of skin 27 and member 3!].

After assembly, the component parts of the. panel are tack welded together to retain them in place during the brazing operation. r

1 .The assembled panel is placed between two sheets 31 and 32 offlexiblesheet metal both of which are of sub-, stantially greaterasize than'skins 26, 27. Sheets 31 and 32 are secured together as by resistance seam welding adapted to receive any suitable fastening means (not 7 along afline extending entirely. around panel 10 as shown at 33 (Fig.5), thus forming asealed envelope 34' containing'the panel. Envelope 34is'p'rovided Wlthfflfl outlettube 35 passing throughsheet 31 and extending along one'side' 'ot the panel within the envelope; The inner end 36 armless isclo'sed'and the portion of the tube within the'enuelope'is provided with spaced apartslots 37 passiugj'threugh the'wall thereof. Envelope 34is also provided With'ari inlet tube38 which passes through sheet 31'andfextends along the opposite side of panel 10 within the envelope. The portion of tube 38 within envelope 34 -isprovided with 'spacedapart openings 39 which are of such size that their combined area; is approximately equal to the cross sectional area of tube 38 and the inner end (not shown) of tube 38 is closed. 'The extending edges 40 ofshe'ets 31 and 32 are secured together and portions cut away as shown at 421to provide a set'of slings 43"adapted to receive weights 44. a -;Envelope 34 containing 'panel 10 is placed on fixture v'elop'e 34 causes the pressure of the ambient atmosphere to rpress sheets 31 and 32 inwardly'against plated skins 26 and 27 thereby forcing the alloy strips 29, 29', into contact with the nickel covered ends of the cells of core 25. Hydrogen gas from source 51'isf permitted to flowthrough tube 38into envelope 34, the rate of flow being. controlled by regulator 52 so that pressure within envelope 34 remains below the pressureof the surrounding furnacaatmos'p'here. The air withdrawn from within envelope 34 enterst'ube" 35 through slots 37 along one sideofpanel .10 and the hydrogen gasadrnitted into envelope 34 leaves tube '38 through openings 39' on the oppo'site side of the panel so that withdrawal of air from 11, as shown inFigs. 5 and 6, with the center of the panel in substantial alignment with the center of lattice 12. a To facilitate this procedure; sheets 31 and 32 areprovided with small openings 45 passing therethrou gh outwardly of seam 33 which are aligned with suitable locating marks (not shown) onffixture ll. Weights44 are placed in slings 43 and permitted to hang down and apply tension to'the edges of envelope 34 thus causing sheet 311m conform to the contour of sheet 17 and sheet 32 to press sheets 26and 27 against icore 25. To prevent damage to envelope 34 and core 25and. its replacement with hydrogen gas takes placequickly. To prevent the pressure within envelope 34 from rising during the brazing 'operation; aspirator 49 remains in operation to continually withdraw a small amountof hydrogen from within en'- velope34, the gas ,being ignited by a pilotflame 5-7 as it leaves aspirator '49 to render. it harmless.

which form passagesconnecting individual cells.

Furnace 46 is. gradually heated by any known type.of heatingmeans (not shown) :to a temperature within the ranger 1700? to, 'l850- E'and electrical current is passed: through coil 54' to heatthe hydrogen gaspassing the edges'of panel 10 from the force with'whichthey are pressed against fixture 11, a rigid supporting member 41 shaped as an undulate stripof metal is placed under the top projecting portion of closure member 30, as

shown in Figs. 5 and '6, tosupport the edges of the panel...

inic'kel' plating ,on sheets '26, 27," ,closur'e .member' 30, 1 doubler 68, and thatEonthe ends of the cells of. core 25.

p the abovedescriptionof fixture 11 the upper surfaceltS of lattice 12;is machined to a'contour adapted to support panellfl which is illustrated as having two curved 'skins 26, 27 resting against-cellular core, 25 the major'por'tion of which-is ofuniforni thickness. {It is to be understood that 'fixturell may be modified to sup-- port a 'panel't he bottom of which isflat. In this case the upper surface of lattice 12 is machined to a plane face to a plane support-tor. flat sheet 17v and 'envelope 34. e

' Referring'to Fig. time ll'suppcr'ti avao t 34 and'panel 19 is placed in a furnace 46 with tubes 35 and;

'38 extending out through an opening 47 in'the wall 48; he??? Oaflfit b r tt h fieae i a e: .5

therethrough. The" hot furnace. atmosphere circulates freely through lattice 12 passing through openings '15 (Fig. 16) in the wallsof cells 14 touuiformly. heat panel 10. Also. due to'the preheating of the hydrogen gas by coils .53land 54 beforeitenters panel '10, the entire panel soon reaches the brazing temperature which causes the several strips of brazing alloy, to melt and adhereto the When the brazing is completed, transformer '56 is disconnected and theflow of hydrogen'rthrough tube 38 stopped. Tubes 35 and 38are disconnected from aspiratorf 49 and hydrogen tank '51 respectively, whereupon fixture ,11 is removed fromthe furnace. Envelope 34 andpanel '10 areallowed jtolslowlycoolto ro'om temperature when the brazed panel isremoved from the envelope. Theibrazing operation having taken place in an atmosphere "free'ofoxygemfall the teompon'ent parts of the'saudwich panerare entirely "free from scale" or To. facilitate withdrawal .ofair froml panel 10,.and .to. permit thehy- V drogen gas to new quickly into. all parts of core'25', the

cell, walls are provided with small holes 58 '(Fig. 4)

operation. The presence of the thin nickel plate on core 25 and skins 26, 27 is found to cause the silver-manganese braze alloy to accumulate at the ends of the cell walls 75 and form strong, thick fillets 76 which securely bond the ends of the cells to the abutting skins. It is found that in the absence of plating the core and skins, the molten braze alloy flows along the cell walls and tends to cover them with the result that most of the alloy is rendered ineffective to bond the parts together. Furthermore the silver in the brazing alloy adheres to the nickel film on core 25 and skins 26, 27 more strongly than it does to the stainless steel of the core and skins. The nickel plating also prevents the steel of the core and skins from contact with the air which would gradually form oxides on the surface of these parts. Such oxides are detrimental in that they prevent the molten braze alloy from reaching the underlying steel and becoming attached thereto.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment of the invention is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claim, and all changes which come within the meaning and range of equivalency of the claim are intended to be embraced therein.

Having thus described'my invention, what I claim as new and useful and desire to secure by Letters Patent is:

A sandwich panel comprising an upper metal sheet having its lower face covered with a thin film of coherent nickel; a lower metal sheet having its upper face covered with a thin film of coherent nickel; a metal core covered with a nickel plating and composed of a plurality of thin walled interconnected cells each having the opposite ends thereof respectively abutting the nickel films or" said upper and lower sheets, said sheets and core being composed of stainless steel; and fillets of silvermanganese brazing alloy brazed respectively to said nickel films on said upper and lower sheets and to the nickel plated sidewalls of said cells at said opposite ends thereof, said silver-manganese alloy consisting of silver and 15% manganese, said alloy having a melting point substantially lower than that of said nickel films and plating and lower than that of the parent metal of said sheets and core so that alloying of the brazing alloy with the nickel and melting of the parent metal are prevented as said fillets are brazed to the nickel covering on said sheets and core.

References Cited in the file of this patent UNITED STATES PATENTS 673,126 Martin Apr. 30, 1901 2,060,608 Butler et al. Nov. 10, 1936 2,297,357 Kelley Sept. 29, 1942 2,417,662 Rosales Mar. 18, 1945 2,464,821 Ludwick et al. Mar. 22, 1949 2,585,043 Sandberg Feb. 12, 1952 2,587,116 Clay Feb. 26, 1952 2,609,068 Pajak Sept. 2, 1952 2,654,946 Rhodes et al. Oct. 13, 1953 2,779,999 Boam et al. Feb. 5, 1957 

